1. Field of the Disclosure
This disclosure relates to a backlight unit, and more particularly to a backlight unit capable of being scan-driven, as well as a liquid crystal display (LCD) device with the same.
2. Description of the Related Art
Cathode ray tubes (CRTs) correspond to one of display devices which are widely used. The CRTs are mainly used as monitors for TVs, measuring apparatuses, information terminals, and others. However, the heavy weight and large size of the CRTs have been a major hindrance to the manufacturing of small, light electronic products.
In other words, the CRTs have the limitations of weight and size in the current trend of small, light electronic products. Under such circumstances, LCD devices using an electro-optical effect, plasma display panels (PDPs) using a gas discharge, electro luminescence display (ELD) devices using an electro-luminescent effect, and so on are expected to substitute for the CRTs.
Among the substitutable display devices, LCD devices are being actively researched. Also, LCD devices are gradually being used in a wide range of applications due to their advantages such as lightness, thinness, and low power consumption. Moreover, LCD devices are being manufactured to have even larger screens, be thinner, and consume less power, in order to meet the requirements of users. Such LCD devices display images by controlling the amount of light transmitted through liquid crystal.
LCD devices are not self-illuminating display devices, unlike CRTs. As such, an LCD device includes a backlight unit provided on the rear surface of an LCD panel. The backlight unit includes a separated light source providing light necessary to display an image. The backlight unit can be classified as either an edge type or a direct type in accordance with the disposition of a light source.
Such an edge type backlight unit is mainly applied to comparatively small-sized LCD devices such as the monitors of laptops and desk-top computers. The edge type backlight unit has good light uniformity, a lengthened lifespan, and the advantage of making the LCD device thinner.
The direct type backlight unit has begun to be concentrically developed as the LCD device is enlarged to a size above 20 inches. The direct type backlight unit forces light to be directly irradiated onto the entire surface of the LCD panel. To this end, the direct type backlight unit includes a plurality of light sources arranged on the lower surface of a diffusion plate. Since the direct type backlight unit has a higher light efficiency than the edge type backlight unit, it is mainly used for LCD devices of a large size which require a high brightness.
The backlight unit employs a plasma type light source, such as a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), an external electrode fluorescent lamp (EEFL), an external and internal electrode fluorescent lamp (EIFL), or others, as a light source. Alternatively, the backlight unit uses a light emission diode (LED) as a light source. Particularly, the LED is widely used in the backlight unit because of its features of long lifespan, low power consumption, small size, superior durability, and others.
The edge type backlight unit ordinarily includes a plurality of LEDs arranged on its side surface, and a light guide plate disposed parallel to the plurality of LEDs. Recently, the edge type backlight unit is being configured to be driven in a scan mode, in order to prevent the generation of a residual image. This scan mode backlight unit divides a screen (for example, an LCD panel) into a plurality of blocks arranged along a direction and sequentially applies light to the blocks.
To this end, the ordinary backlight unit of the scan mode forces the plurality of LEDs positioned at its one side to be sequentially lightened in a fixed-size division. Also, the ordinary backlight unit guides light emitted from the plurality of LEDs to the divided blocks on the LCD panel using the light guide plate. However, emitted light from the LEDs is diffusively reflected when it enters the light guide plate. Due to this, it is very difficult for the backlight unit to drive in the scan mode.
On the other hand, a light guide plate with guide patterns formed on its upper and lower surfaces is being used in the ordinary LCD device, in order to guide light to each of the divided blocks. It is also difficult for the patterned light guide plate to prevent the diffused refection of light.